U.S. patent number 5,766,496 [Application Number 08/656,498] was granted by the patent office on 1998-06-16 for decapsulator and method for decapsulating plastic encapsulated device.
This patent grant is currently assigned to Nisene Technology Group, Inc.. Invention is credited to Kirk Alan Martin.
United States Patent |
5,766,496 |
Martin |
June 16, 1998 |
Decapsulator and method for decapsulating plastic encapsulated
device
Abstract
An apparatus and method for selectively etching an encapsulant
forming a package of resinous material around an electronic device
includes a etchant solution source and an etching assembly
including an etch plate and a movable cover forming an etching
chamber. An etch head is supported by the plate and the device
package is mountable in the chamber on the etch head. A first
syringe pump pumps a first quantity of etchant into the etch head
and a second syringe pump agitates or oscillates at least part of
the first quantity of etchant repeatedly into and out of an etched
cavity formed on the package exterior surface by reaction of the
etchant solution with the resinous material. A waste outlet and
reservoir extends from the etch head. The etch head is attached to
an alumina ceramic heat exchanger including a spirally grooved
passageway formed by an inserted core to heat a small volume of
etchant immediately prior to introduction of the etchant against
the package and subsequent oscillation.
Inventors: |
Martin; Kirk Alan (Aptos,
CA) |
Assignee: |
Nisene Technology Group, Inc.
(Santa Cruz, CA)
|
Family
ID: |
24633286 |
Appl.
No.: |
08/656,498 |
Filed: |
May 31, 1996 |
Current U.S.
Class: |
216/56;
156/345.18; 216/90; 216/92 |
Current CPC
Class: |
H01L
21/67075 (20130101); H01L 21/67126 (20130101) |
Current International
Class: |
H01L
21/00 (20060101); B44C 001/22 () |
Field of
Search: |
;156/345L,345LS,637.1,639.1 ;216/38,56,90,92
;438/745,747,748,749 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Brochure entitled: "B&G Decapsulator", Model 250,B & G
International, Soquel, California (6 pages), pre-May 1995..
|
Primary Examiner: Powell; Williaim
Attorney, Agent or Firm: Skjerven Morrill MacPherson
Franklin & Friel MacDonald; Thomas S.
Claims
I claim:
1. An apparatus for selectively etching an encapsulant forming a
package of resinous material around an electronic device
comprising:
a source of etchant solution;
an etching assembly including an etch plate and a movable cover,
said etch plate and cover forming an etching chamber;
an etch head supported by said etch plate, wherein an electronic
device package is mountable in said chamber on said etch head;
a first pump for pumping a first quantity of etchant solution into
said etch head;
a second pump for agitating at least part of the first quantity of
etchant solution into and out of an etched cavity formed on an
exterior surface of the electronic device package by reaction of
the etchant solution with the resinous material; and
a waste outlet extending from said etch head to disposal.
2. The apparatus of claim 1 wherein said first pump and said second
pump are syringe pumps, the second pump incrementally pumping a
smaller volume of etchant solution than the first pump.
3. The apparatus of claim 2 further comprising a supply line
extending from said source of etchant solution to said etch head,
said first and second pumps each being in separate flow connection
to a supply line;
a valve in said flow line between the flow connections of said
first and second pumps, wherein when said valve is open, a supply
of etchant solution fills the flow line upstream of the first pump
flow connection upon operation of the first pump and, when said
valve is closed, a first portion of the first quantity of etchant
solution in the flow line upstream of said valve is moved back and
forth into and out of said second pump and a second portion of the
first quantity of etchant solution is moved through said etch
head.
4. The apparatus of claim 3 further comprising a heat exchanger
block including an etchant solution inlet connected to said flow
line, said etch head being in flow connection to said heat
exchanger block, and a heat exchanger within said heat exchanger
block and including a flow passage in flow connection to said
supply line.
5. The apparatus of claim 4 further comprising a heater block
concentrically surrounding and in contact with an exterior
peripheral portion of said heat exchanger block, said heater block
including at least one heater for heating said heater block, such
that heat from said heater and said heater block heats said heat
exchanger and etchant solution flowing through said heat exchanger
to said etch head.
6. The apparatus of claim 5 wherein said heat exchanger block and
said heat exchanger are constructed of alumina ceramic material and
said heater block is constructed of aluminum material.
7. The apparatus of claim 6 wherein said ceramic material is about
99.8 weight percent of alumina.
8. The apparatus of claim 7 wherein said etchant solution inlet
includes a ceramic tube, O-ring sealed in said heat exchanger
block.
9. The apparatus of claim 4 wherein said heat exchanger and such
flow passage comprises a cylinder having an exterior spiral groove,
said cylinder being in press-fitted connection in said heat
exchanger block, said groove extending spirally in a direction of
parallel to a longitudinal axis of said etchant solution inlet and
said heat exchanger block.
10. The apparatus of claim 3 further comprising a heat exchanger
block including an etchant solution inlet connected to said flow
line, said etch head being in flow connection to said heat
exchanger block inlet, and a heater block concentrically
surrounding the heat exchanger block.
11. The apparatus of claim 10 wherein said heater block comprises a
pair of block halfs in spring-pressed connection against said heat
exchanger block.
12. The apparatus of claim 1 wherein said etch head includes a
demountable cylindrical plug O-ring sealed in said etch plate, said
plug having a passageway extending through said plug in flow
connection to said source of etchant solution and wherein the
electronic device package is mounted on a surface of said plug
facing said etching chamber.
13. The apparatus of claim 12 further comprising an etch disk in a
surface of said cylindrical plug and outwardly facing said etching
chamber, said etch disk having an orifice for etching away a shaped
hole through the exterior surface of the electronic device
package.
14. An apparatus for selectively etching an encapsulant forming a
package around an electronic device comprising:
a source of etchant solution;
an etching assembly including an etch plate and a movable cover,
said etch plate and cover forming an etching chamber;
an etch head supported by said etch plate, wherein an electronic
device package is mounted in said chamber on said etch head;
and
wherein said etch head includes a cylindrical plug, O-ring sealed
in said etch plate, said plug being demountable from said etch
plate in a direction facing said etching chamber, said plug having
a passageway extending through said plug in flow connection to said
source of etchant solution and wherein the electronic device
package is mounted on a surface of said plug facing said etching
chamber.
15. The apparatus of claim 14 further comprising an etch disk in a
surface of said cylindrical plug and outwardly facing said etching
chamber, said etch disk having an orifice for etching away a shaped
hole in the exterior surface of the electronic device package.
16. The apparatus of claim 14 further comprising a first syringe
pump in flow connection between said source of etchant solution and
said etch head for moving a volume of etchant solution into and out
of said etch head and a second syringe pump for agitating said
volume cyclically against an exterior of an electronic device
package positioned on said etch head.
17. The apparatus of claim 14 wherein said cylindrical plug
includes a cylindrical groove extending in a plane above a plane of
said etch plate for finger grasping and removal of said cylindrical
plug from said etch plate.
18. A method of decapsulating a plastic package of resinous
material surrounding an encapsulated electronic device
comprising:
providing a source of etchant solution and an etching assembly
including an etch plate and a movable cover, and an etch head in
flow connection to the source of etchant solution;
positioning an electronic device package of resinous material on
the etch head;
pumping a volume of etchant solution from the source of etchant
solution to the etch head;
oscillating at least a portion of the volume of etchant out of and
back into the etch head; and thereby digesting the resinous
material to form a hole in said package.
19. The method of claim 18 further comprising the steps of
performing a series of oscillating cycles and then repeating the
pumping step.
20. The method of claim 19 wherein said series of oscillating
cycles in number are from 5 to 20 cycles prior to the repeating the
pumping step.
21. The method of claim 18 further comprising pumping a sufficient
volume of etchant fluid such that a portion of the volume exits to
waste.
22. The method of claim 21 wherein from about ten to about twenty
pumping steps are performed prior to the waste reaching a waste
reservoir.
23. An apparatus for selectively etching an encapsulant forming a
package of resinous material around an electronic device
comprising:
a source of etchant solution;
an etching assembly including an etch plate and a movable cover,
said etch plate and cover forming an etching chamber;
an etch head supported by said etch plate, wherein an electronic
device package is mountable in said chamber with respect to said
etch head;
a first pump for pumping a first quantity of etchant solution into
said etch head; and against an exterior surface of the package;
a second pump for agitating at least part of the first quantity of
etchant solution into and out of an etched cavity formed on the
exterior surface of the electronic device package by reaction of
the etchant solution with the resinous material; and
a waste outlet extending from said etch head to disposal.
24. The apparatus of claim 1 wherein said first pump and said
second pump are syringe pumps, the second pump incrementally
pumping a smaller volume of etchant solution than the first pump.
Description
FIELD OF THE INVENTION
The present invention relates to an apparatus and method for
applying an etchant to a plastic encapsulated device, particularly
to an epoxy encased semiconductor chip, to provide access to the
device or chip for internal visual inspection, test and repair.
BACKGROUND OF THE INVENTION
Plastic packaging of various electronic devices including
semiconductor chips have been employed for some years. Typical an
epoxy resin is molded around the chip, a central portion of a lead
frame and bonding wires or other connections between contact pads
on the chip to inner lead fingers on the lead frame. It is often
desirous to decapsulate the package at least in part to allow for
inspection, test and repair of the chip and the wire bonds to the
chip and inner lead fingers, after the epoxy covering these
elements is safely and effectively removed.
Commonly, concentrated acids such as sulfuric and nitric acids or
other solvents for the resin have been employed. Problems in prior
art decapsulators and methods include difficulty in controlling the
desired amount of etching, in removing debris formed in the etching
process, prevention of damage to the package including interior
metallization and providing for adequate safety.
An early patent in the decapsulator art is Wensink U.S. Pat. No.
4,344,809 where a jet etch apparatus includes an etching block and
a jet pump provides for etchant flow.
A Decapsulator sold by B&G Enterprises, Inc. of Soquel, Calif.,
namely a Model 250, includes an appropriate acid resistant gasket
seated on an etch head and the device to be decapsulated is placed
on the gasket. A safety cover closes automatically when the process
is started, clamping the device in place. The gasket on the etch
head allows the chamber to be sealed and pressurized with nitrogen
to approximately two PSI. The etching is started when a metering
pump moves etchant from a heat exchanger located in plate with a
sinuous passage into a cavity formed by the gasket, the device and
the etch head. The acid remains in the chamber for a short period
of time, where it reacts with or attacks the encapsulant material.
After the etchant has been allowed to work, the pump is activated
again and a fresh volume of acid is moved into the cavity. This
process continues until the desired amount of device exposure is
achieved. When the integrated circuit is exposed at the end of the
etch cycle, the pump runs continuously to flush the cavity. After
this rinsing period the entire system is purged with nitrogen,
blowing all waste materials into the waste bottle. At the end of
the process, the safety cover opens automatically and the device is
removed for post-etch cleaning.
U.S. Pat. No. 5,252,179 discloses a method and apparatus for
selective spray etching of an epoxy encapsulated chip. A diaphragm
can be raised or lowered to direct flow of etchant, and debris is
removed without moving the chip from the chip carrier. Used etchant
is collected and recycled. U.S. Pat. No. 5,127,991 shows a process
for an etching copper sheets in which a pumped source of etchant is
heated. U.S. Pat. No. 5,271,798 shows an etching process for
tungsten residue on a semiconductor wafer including a sealed
apparatus with an etchant inlet port and suction removal of etching
byproduct.
In at least some of the prior art devices various deficiencies have
been encountered. For example, a fixed etch head is provided which
limits the area of the package which is to be etchant attacked;
external auxiliary heaters must be used to heat the etchant;
excessive etchant fume or seepage limit seal life; there is
inefficient removal of etching debris; a particular slowness of the
etching process is present due to non-reactive materials at the
etch face; and there is a lack of keeping acid consumption low.
SUMMARY OF THE INVENTION
The present invention relates to an apparatus and method for
decapsulation of a packaged electronic device where an oscillatory,
agitating flow of etchant is provided in an etching cavity for
removal of non-reactive elements of the epoxy resin from the etch
face resulting in the exposure of more of the reactive material for
faster etching. The effect reduces the etch time, the total cycle
time due to reduced line fill time and a shorter etchant heat time,
while keeping acid consumption low. In one embodiment an
interchangeable etch head is provided which allows easy
substitutions of etching area styles, that is the size and shape of
the package area on which the etchant will attack and etch away the
resin. The reduced etchant heat time is accomplished by providing
an alumina ceramic heat exchanger block, with an acid inlet port, a
waste outlet port and an alumina ceramic, grooved cylinder heat
exchanger or multiple holed alumina block in flow connection to the
inlet port, and a surrounding aluminum heater block containing at
least one resistance heater. Thus only a relative small volume of
etchant need be heated immediately prior to the flow of the etchant
against the package, lessening the overall decapsulating time.
The apparatus for selectively etching an encapsulant forming a
package around an electronic device includes a source of etchant
solution; an etching assembly including an etch plate and a movable
cover, the etch plate and cover forming an etching chamber; and an
etch head supported by the etch plate. An electronic device package
to be decapsulated is mounted in the chamber on the etch head. A
first pump is provided for pumping a first quantity of etchant
solution into the etch head and a second pump provided for
agitating the first quantity of etchant solution into and out of an
etched cavity formed on an exterior surface of the electronic
device package. Debris from the etching of the package is forced
through a waste outlet extending from the etch head to a waste
reservoir. In a preferred embodiment, the first pump and the second
pump are syringe pumps.
In another embodiment an apparatus for selectively etching an
encapsulant forming a package around an electronic device includes
a source of etchant solution; an etching assembly including an etch
plate and a movable cover, the etch plate and cover forming an
etching chamber; and an etch head supported by the etch plate. An
electronic device package to be decapsulated is mounted in the
chamber on said etch head. The etch head includes a demountable
cylindrical plug, O-ring sealed in the etch plate, the plug having
a passageway extending through the plug in flow connection to the
source of etchant solution. The electronic device package is
mounted on a surface of the plug facing the etching chamber.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic side view partially in section of the overall
encapsulation apparatus.
FIG. 2 is a top view of the two-pump subsystem and etchant solution
valving.
FIG. 3 is a cross-sectional view of the etch head assembly with an
integrated circuit chip mounted on the etch head for
decapsulation.
FIG. 4 is an exploded perspective view of the etch head mount for
the encapsulated device.
FIG. 5 is a cross sectional view of the agitation syringe with
associated metering sensors.
FIG. 6 is a cross-sectional view of a modified form of the etch
head assembly including the heater blocks and the heat exchanger
block.
FIG. 7 is a partially cut-away end view of the heater blocks.
DETAILED DESCRIPTION
FIG. 1 shows a decapsulating system 10 including an etch head
assembly 20 including an etch plate 21, and movable cover 22
clamped on by clamps 22a or otherwise pivoted by structure (not
shown) to the etch plate. A spring pressed holder 23 with a ram
nose 23a holds the electronic device package 3 (FIG. 3) to be
decapsulated against an etch head top surface 25a and gasket or
seal 5. The etch head 25 includes an etchant solution inlet passage
11 and waste outlet passages 12 (FIG. 3) leading to a waste bore 15
in a heat exchanger block 26. Block 26 abuts the bottom of the etch
head 25 and includes a heat exchanger core 27 having a spirally
grooved exterior forming with the walls of a bore 14 in block 26 a
spiral passageway 17 for heating etchant solution flowing through
the passageway. A heater block 28 including one or more resistance
heaters 29 (FIG. 6), concentrically surrounds the cylindrical
periphery of heat exchanger block 26. The passageway 17 extends
spirally in parallel to the longitudinal axis 8 of block 26 and
etch head 25.
In one embodiment as shown in FIG. 3 the etch head 25 is in
press-fitted engagement within a bore 9 in etch plate 21. The etch
head contains a cylindrical peripheral groove and O-ring 6 which
seals the etch head in the etch plate. A second O-ring 2 seals heat
exchanger block 26 in bore 9. A second cylindrical groove 7
extending in a plane above the plane of the etch plate, functions
as a finger-grasping groove for manually and easily removing the
etch head from bore 9 for replacement, when desired, with an etch
head having a different size or shape of exit orifice. For example
a cross-shaped orifice can be used to better reach the corners of a
rectangular package interior with the agitating stream of acid.
FIG. 4 illustrates the top 25a of the etch head 25 with a straight
etch orifice 25b therein. A gasket alignment ring 5 and a cavity
definition etch disk or gasket 4, as used in the Model 250
Decapsulator is employed for mounting the device 3.
Referring back to FIGS. 1 and 2, a first acid-resistant syringe
pump 30 operates as a positive displacement pump utilizing a
standard syringe as the displacement cylinder and piston. The
syringe is connected to a first flow valve 31 in a flow line 32
which extends to the heat exchanger block 26.
To eliminate any problems resulting from non-pulsing flow, a second
acid-resistant syringe pump 40 is positioned upstream of valve 31
and in connection to flow line 32 to introduce an oscillating flow
of etchant solution. This pump 40 will, during the etching portion
of the process, keep moving acid into and out of an etched cavity
3a being continually formed on the package exterior which is
exposed to the etchant or digester of the package encapsulant and
which action eventually provides the desired cavity in the package.
This will create an effective flow rate
(milliliter.backslash.minute), for example, sixty times the volume
of the agitator syringe when the syringe is cycled once per second.
The effective flow rate is high enough to remove all etch debris
and gas from the cavity formed by the etching. Once the volume in
flow line 32 fills the passageways in the heat exchanger block, the
additional increments of acid introduced by pump 30 carry the
resultant debris from the etching zone (cavity) to a waste
reservoir 33, such as a waste bottle.
The agitator syringe 40, with valve 31 shut closed, will create
effective flow rates and agitation against the package being
decapsulated, while keeping acid consumption low. The agitator
syringe preferably will swish back and forth a smaller volume, for
example 1/2 milliliter, than the main pump syringe 30 increment(s)
which, for example, will inject 2.5 ml. of etchant solution. Both
of these syringes normally have a limited plunger life but are easy
and inexpensive to service. Any seepage around the plunger is
controllable to a workable level. The fixed volume of the main
syringe 30 injection will be no problem since the addition of acid
increments and the action of the agitator syringe 40 produces the
necessary flow to remove debris. On packages that etch very slowly,
the flow rate can be reduced accordingly. In typical use there
should be no situation where more than 10 ml. of acid is
required.
The maintenance cycle for the system will be limited by the
operational life of the syringe plungers and the pneumatic air
cylinder O-rings. All of the wear related parts are made to allow
easy replacement during the periodic maintenance procedure. The
overall system life will be determined by the control valve
diaphragms and spring life.
Second and third valves 34 and 35 are in flow connection with flow
line 32 and to respective sources 36 and 37 of etchant solution,
such as sulfuric acid or nitric acid, in particular fuming nitric
acid, respectively.
A fourth valve 38 in flow line 32 is connected to a nitrogen gas or
other inert gas supply 56 as shown in a prior art gas sub-system 52
to supply inert gas for conveying debris to waste as needed and for
supplying initial pressurization inert gas through a fifth valve 39
to a chamber 24 between the etch plate 21 and cover 22. A sixth
valve 50 is openable to purge the chamber of initial oxidizing gas
or air and of any etching debris occasioned by leakage past the
held device 3 into chamber 24. Valve 50 allows venting of chamber
24 to waste reservoir 33 for disposal. A standard high pressure
regulator 53 and a standard low pressure regulator 54, as used in
the prior art Model 250 decapsulator, supplies debris purging gas.
About 40 psi of nitrogen gas is supplied by line 55 to operate the
pneumatic controls (not shown) for the various valves.
To effectively transport etch debris and create a clean cavity, a
flow rate of 25 to 30 ml per minute of acid is required. To
establish a 30 ml per minute flow rate from the agitator syringe,
with a 2 second full cycle time, requires a 0.5 ml agitator
syringe. A 0.5 ml agitator volume requires a heat exchanger core
with at least 1 ml total volume to keep the agitated volume heated
while bringing the next increment of pumped etchant from pump 30 up
to temperature in the range of 70.degree.-240.degree. C. depending
on the acid used and other process parameters. In addition, the
waste side of the etch head assembly preferably has a heated volume
of at least 0.5 ml. Since the pump syringe 30 is isolated from the
agitator syringe 40 by a valve 31, it need only have the
displacement required to fill the system from the syringe to the
device package. With the valve 31 isolated, the pump 30 can be
drawing in acid from a source bottle 36 or 37 while the agitator
syringe 40 is agitating the active volume of acid.
The etch process proceeds as follows.
1. The syringe pump 30 draws in a full volume from the acid source
bottle. The agitator syringe 40 is at zero volume and all lines are
clear of acid.
2. The syringe pump 30 fills the lines 32 from valve 31 to the heat
exchange block and in the etch head up to the device package
surface abutting the etch head.
3. After the acid heats to etching temperature in the heat exchange
core passageway 17, the syringe pump 30 moves an additional 0.5 ml
(the volume of the agitator syringe) into the system.
4. With valve 31 closed the agitator syringe 40 is activated
drawing in its full volume from the heat exchanger block in one
second and returning the "agitating" volume in the next second.
These cycles continue typically for 5-20 cycles until the acid
reaches its carry capacity. "Carry capacity" as used herein means
the amount of debris that the acid can contain and still allow flow
of the resultant slurry, without plugging of the various flow
passages.
5. The agitator syringe 40 is returned to the zero volume position
and the syringe pump 30 moves another 0.5 ml of acid into the
system.
6. Steps 4 and 5 are repeated as required. Typically about 16
cycles are needed to effect movement of waste acid to the waste
bottle 33. If the syringe pump 30 volume is exceeded, it will draw
more acid from the source bottle during the agitation portion of
the cycle. During the last agitation cycle, the syringe pump 30
draws a rinse volume from the source bottle.
7. After the device is fully etched to form a decapsulated aperture
3a (FIG. 3) in the device package and exposure of the wire bonds,
for example, the agitator syringe 40 returns to the zero volume
position and the syringe pump 30 moves the rinse volume into the
system. At the end of the rinse pumping cycle, both pump valves 31
and 38 are opened and the entire system is cleared of acid with dry
nitrogen from the N.sub.2 system 52. Valves 39 and 50 may also be
opened to allow flushing of the chamber 24 with nitrogen. It is
desired that chamber 24 be an inert environment with no oxygen or
water present. Some residual acid will be left in the syringes and
valve dead volumes. This may require an acid flush cycle when
changing from one acid to the other.
Etching small devices may require only one agitation cycle and the
time of the cycle needs to be programmable to control the total
etch time. The minimum acid used to etch a part is determined by
the fill volume, the agitation syringe displacement, and the
minimum rinse volume. The maximum acid consumed is simply a
function of the carry capacity of the acid and the volume of
material to be removed. Etching low etch rate plastics requires
more time, not more acid as the agitation cycle time can be
increased to insure complete use of the acid.
The increased agitation in the etched cavity will reduce the total
etch time required, particularly for large devices. The constant
movement of acid into and out of the etched cavity will be more
efficient at removing non-reactive materials, e.g. carbon or glass
particles in the plastic encapsulant, from the etched face exposing
more reactive material for etching. Even if this does not reduce
the etch time for normal devices and plastics, the total cycle time
will be reduced because of the reduced fill time and the
elimination of any device heat up time. As the acid is heated both
in the heat exchanger and the waste tube, the agitation will
efficiently transfer heat to the device. This will allow for faster
heating than some current etchers where the heat up time currently
is determined by the thermal conductivity of the gasket. Using the
acid as the heat transfer medium will require that the first
agitation cycle be increased in time as there will be little
etching until the acid has heated the device up to the etch
temperature. In the prior art Model 250, the minimum heat up time
is 50 seconds. Twelve seconds of this is required to lower the
safety cover and purge and pressurize the chamber. The remainder of
the heat up time is required to fill the heat exchanger, heat the
acid, and preheat the device being etched. With the syringe system
of this invention, the fill time will be one to two seconds, the
acid heat time will be about six seconds, and then agitation can be
started. This will reduce the total cycle time by thirty seconds
down to about 20 seconds.
Some of the control functions for the syringe pump 30 and agitator
syringe 40 lend themselves well to local control. The agitator
syringe with its two position sensor needs to run at its own rate
as determined by the exhaust relief valves on a pneumatic control.
The pump syringe stroke in pump 30 is controlled to draw and
discharge fixed amounts of acid as determined by a minimum of six
position Hall-sensors 46 as seen in FIG. 5. Two spaced Hall-sensors
may be used to determine the fixed stroke of the agitation syringe
40, particularly that the agitation syringe is operating at its
proper stoke. Fiber-optic sensors (not shown) may also be utilized.
The activity of the pump syringe 30 preferably is synchronized with
the operation of the agitator syringe 40. A small local processor,
such an a PIC 16C55 processor available from Microchip Technologies
of Chandler, Ariz., as is known in the art is used to control the
pump and agitator functions. The control electronics are
distributed between the multi-controller and the processor in the
etcher unit. The multi-controller provides the user interface and
the supervisory control of the etcher unit. A temperature control
subprocessor (not shown) measures the output of the
thermocouple-type resistor, ambient temperature, line voltage, and
current into the heaters. It adjusts the current into heaters based
on the difference between the desired temperature of the heat
exchanger and the actual temperature thereby controlling the heat
exchanger temperature. A multi-controller (not shown) is used to
send commands to the local processors and the local processor
performs the actual pump and temperature control.
Etchant selection, safety equipment for the operator, unit set-up
details of a typically used controller modified for use with the
dual syringes of the invention, and general mechanical and
electrical operations of a typical decapsulator are in the Model
250 operation, installation and service manual, the content of
which are incorporated herein by reference.
The pump assembly includes the syringe pump 30, the agitator
syringe 40, acid selection valves, and the associated fittings and
plumbing. The assembly is mounted on a plate that will separate the
acid from the clean side of the etcher unit. Only pneumatic control
lines will pass through the plate and no electronics will be
mounted on the acid side. All components, other than springs,
screws, and syringe plunger shafts, will be made of Teflon.RTM.,
glass, polypropylene, or PVC or other acid-resistant material. All
metal components, where possible, are made of stainless steel.
As shown in FIG. 5 the syringe 41 per se is driven by two separate
air cylinders 42 and 43. Nitrogen is fed into the feed cylinder 42
drawing fluid into the syringe 41. The return cylinder 43 is
pressurized to force fluid from the syringe. A magnet 44 is placed
in a rod clamp 45 to activate Hall-effect position sensors 46. The
control pressure to the cylinders is fed from the mounting face
eliminating plumbing from the acid side. A piston 47 made of Teflon
plastic because of its wear resistance and natural lubricity
extends between the cylinders. All other components, other than the
syringe, are made of PVC because of its strength and acid
resistance. Two syringe pumps and two manifold valve assemblies
make up the complete pump assembly. A three valve manifold provides
acid and nitrogen selection. All three valves are normally closed
and pneumatically activated. All manifold ports are the standard
1/4-28 thread. The second manifold contains only normally closed
valve and interconnects syringe Luhr fittings (not shown) with the
inlet and outlet.
Acid flow is in direct contact with the heat exchanger. The heat
exchanger core 27 is a spirally grooved (on the outside) cylinder
that is in press-fitted connection in the heat exchanger block 26.
The acid flows through the passageway 17 from the inlet fitting to
the etch head. Because the acid is in direct contact with the heat
exchanger and block, it heats up very fast requiring only a small
acid volume in the heat exchanger core. The heat exchanger core and
the heat exchanger block both are made of 99.8% alumina ceramic,
allowing for both high thermal conductivity and acid resistance.
The heat exchanger is removable for cleaning after the etch head
has been removed.
As seen in FIG. 6 and FIG. 7 the heat exchanger block 66 is clamped
between two heater blocks 28a and 28b in another embodiment of the
heater block and heat exchanger block in FIG. 6. The heater blocks
28a and 28b each contain a cartridge heater 29. The heater blocks
are made of aluminum. The heater blocks are bolted together and
spring loaded by Belleville washers 70 or the like to maintain
contact of the heater blocks with the ceramic heat exchanger block,
while being allowed to expand when heated. For clarity purposes a
gap is shown at this interface between the heat exchanger block and
the heater blocks. Bolts 73 secure the heater blocks and holes 71
are provided to bolt the entire assembly to the etch plate. These
bolts may be threaded into O-ring sealed nuts (not shown) that pass
through the etch plate. The inlet and outlet ports are ceramic
tubes 61, sealed by O-rings 63 into the heat exchanger block 66 and
secured by the heater blocks 28a and 28b. These tubes allow for
some thermal isolation so that standard Teflon transition fittings
can be used to attach tube couplings 64 and O-rings 62 and Teflon
tubing used in the remainder of the unit. All O-rings are
Kelrez.RTM. material for its temperature range and acid resistance.
In this embodiment the acid is conveyed through a central annulus,
a set of four circular holes forming an inlet 65, and waste acid
with etching debris conveyed away from the cavity 3a in the chip 3,
through slightly modified etch head passages 69 and through outlet
circular holes 67 in the heat exchanger 66 to waste (arrows
68).
The above description of the preferred embodiments of this
invention is intended to be illustrative and not limiting. Other
embodiments of this invention will be obvious to those skilled in
the art in view of the above disclosure.
* * * * *